This invention relates to a CDMA (Code Division Multiple Access) cellular system, and in particular, to a radio channel control apparatus which is used in a base station of the CDMA (Code Division Multiple Access) cellular system.
Generally, a mobile communication system such as mobile telephone system employs a cellular system. The cellular system has a service area which is divided into a plurality of cells. A plurality of base stations are respectively arranged in the cells. Each of the base stations can communicate with mobile stations which are located in each of the cells at the same time in a multiple access fashion.
A frequency division multiple access (FDMA) system and a time division multiple access (TDMA) system are often used in the mobile communication system so that the mobile communication system attain the multiple access fashion.
Recently, attention is focused upon a code division multiple access (CDMA) system. This is because the code division multiple access (CDMA) system is achieved by spectrum spreading using a spread code which is different for each channel, and thereby has high efficiency in frequency utilization.
In a CDMA cellular system, a quality of communications between the base station and the mobile stations is gradually deteriorated with an increase of a traffic. Accordingly, the traffic is restricted by the base station so that a required quality level is maintained in the cell.
A conventional radio channel control apparatus is equipped in each of the base stations. The conventional radio channel apparatus detects the traffic in the cell and compares the traffic with a predetermined value. When the traffic is larger than a predetermined value, the conventional radio channel apparatus inhibits a new call origination.
In the CDMA cellular system using conventional radio channel control apparatuses, there is a case that the call origination is inhibited under restriction of the traffic by one of the base stations in the cell while an adjacent radio station have a sufficient traffic handling capacity. Thus, although the overall CDMA cellular system has a spare capacity for the traffic, communication is limited.